Method and system for computer assisted surgery

ABSTRACT

A method and system for computer assisted orthopedic feedback of at least one surgical object relative a pre-operative plan are disclosed. The pre-operative plan includes a virtual object, which is the virtual representation of the surgical object, and a virtual structure, which is the virtual representation of the patient structure. The method comprises providing the pre-operative plan including planned position and orientation of the virtual object relative to of the virtual structure; obtaining the position of the patient structure based on a surface of the patient structure using a surgical navigation system; obtaining the position of the surgical object using the surgical navigation system; registering the patient structure to the virtual structure and the surgical object to the virtual object; tracking a current position and orientation of the surgical object using the surgical navigation system; and providing feedback of a current position and orientation of the surgical object relative to the planned position and orientation of the virtual object based on the tracked current position and orientation of the surgical object.

FIELD OF THE INVENTION

This invention pertains in general to the field of tracking movement ofa surgical object. More particularly, the invention relates to trackingthe position of the surgical object relative a planned position of thesurgical object within a pre-operative plan. Feedback is provided of theposition and orientation of the surgical object relative to a virtualrepresentation thereof in the pre-operative plan. Any deviation betweenthe two may be indicated to the surgeon.

BACKGROUND OF THE INVENTION

Various Computer Assisted Orthopedic Systems (CAOS) tools exist, whichrange from active robotic to passive or navigation systems. Activerobotic systems are capable of performing surgery autonomously withoutinteraction of the surgeon. Many times, the surgeon wants to be incontrol of the surgery, wherein the passive or navigation systems arepreferred, which provide additional information during a procedurecompared to conventional surgery but do not perform the surgical action.The surgeon controls the intervention but acts on additional patientinformation obtained from a pre-operative scan.

For an orthopedic intervention using a CAOS system, a pre-operative planmay or may not precede the actual surgery. One such system is thedevelopment of a surgical template, also referred to as a surgicalguide, to be used during surgery to guide the surgical tools. Thepre-operative plan may aid the surgeon to take decisions about thesurgery before it commences. The pre-operative plan may be based on athree-dimensional scan of the patient, such as a CT or MRI scan. Duringplanning, the surgeon will have access to the internal structures of thepatient to plan the surgery, for example by volumetric scan data thatcan be displayed slice by slice, from various angles, etc. Planned pathsof instruments relative to patient data are transferred to the surgicaltemplate. During surgery, the surgical template guides the path of theinstrument. Hence, the system offers little flexibility for the surgeonto deviate from the planned path should that be necessary during thesurgery. However, this is one way of physically integrating thepre-operative plan with the actual surgery. A benefit of the system isthat the physical components do not need to be calibrated before surgerycommences.

Robotic surgery is another possibility to carry out a pre-operativelyplan. During the surgery, the surgical instrument is not in the hands ofthe surgeon but carried by a robot, which is only indirectly controlledby the surgeon. Since the physical components such as a camera and arobotic arm, are provided as an integrated unit, calibration between thecomponents is not necessary. Therefore, these systems are not onlycostly, but their flexibility is limited by the degrees of freedom andlimited feedback to the surgeon to take corrective actions.

Common to robotic surgical systems is that they use a navigation systemto guide the robot. Such navigation systems can comprise three majorcomponents: the surgical aspect, the virtual aspect, and the navigator.The surgical aspect is the bones and accompanying tissues in thesurgical field. The virtual aspect is the virtual representation of thesurgical aspect. Finally, the navigator establishes a coordinate systemin which the location and orientation of the target as well as“end-effectors” are expressed. The “end-effectors” can be surgicalinstruments or active devices used during surgery.

Three major procedural requirements are essential to successfulnavigation. First, end-effectors must be calibrated for correctrepresentation of their shapes and geometry in the coordinate systemestablished by the navigator. Second, “registration” establishescorrespondence between the surgical and the virtual aspect. Finally,“dynamic referencing” using dynamic reference bases establishes a localcoordinate system that compensates for possible motion of the navigatoror the surgical aspect during surgical action.

Examples of robotic surgical systems are the RoboDoc surgical system,the Acrobot system, and the CASPAR system. Common to them is that theyuse pre-operative and intraoperative data obtained through computernavigation to control the performance of the robot. In these systems,the surgical aspect is registered in the coordinate system of the robotto provide correspondence between the virtual and the surgical aspect,and the actions of the robot is controlled by the virtually planned pathor movements of virtual end-effectors. The position of the robotic armis known in its coordinate system. This makes it possible to also have afixed relationship between the coordinate system of the robot and thecoordinate system of the plan for the surgery, and further calibrationis not required.

Patient anatomical landmarks can be identified by cameras while thepatient is positioned within reach of the robotic arm. In thepre-operative plan, the same anatomical landmarks are present. Thepre-operative plan contains planned movement of end-effectors relativethe anatomical landmarks. During surgery, the same anatomical landmarksare identified and movement of the robot can be controlled in relationthereto based on the plan data to position orthopedic implants. Thesurgery is restricted by the operating range of the robot. Thepre-operative plan may be implemented by the robot, whereby theend-effectors are completely controlled by the plan data, such as in theRoboDoc system. Alternatively, the plan data can be used to apply activeconstraints, as in the Acrobot system, such that the surgeon is assistedto achieve accurate cuts and paths while ensuring the pre-operative planis followed. Common to these systems is that the surgeon is more or lessrestricted by the robotic system, and is not fully free to make his ownchoices during surgery.

Attempts to use Stereotactic surgery for surgical interventions havebeen made. However, the difficulty to obtain a reliable bone referencehas limited this type of surgery to brain surgery. Before scanning thepatient, a frame is attached to the scull of the patient. The frame isused as a fiduciary marker to register the patient to the scan dataduring the surgery, and to track the position of a surgical instrumentto the reference frame, and, thus, to the patient data. During thesurgery, the tip of a probe can be tracked and related to the patientscan data. However, systems using artificial landmarks that are presentduring scanning, such as CT and/or MRI scanning, as well as duringsurgery for registering patient scan data to patient data are not usefulfor orthopedic surgery. An example of such as system is for exampledescribed in WO 96/11624. During the surgery, these systems relatepatient scan or segmented data, such as in the form a 3D representationof the scan data, to the tracked position of the surgical instrument toprovide additional information to the surgeon, such as intraoperativemeasurement tool and tracking of tools with respect to bony anatomydisplayed on the screen, and act on information in a timely manner.However, the purpose of these systems is to provide information aboutanatomical structures that otherwise would not be visible to thesurgeon, but do not give any guidance. Recently, attempts have been madeto rely on anatomical landmarks rather than artificial landmarks for theregistration of the patient's image data set to the position of theinstrument. However, these systems are still limited to displaying thepatient image data relative to the position of the surgical instrument.Also, the data displayed are intrinsic to the patient scan data, and donot relate to the planning of an implant.

Orthopaedic surgery MIS (Minimally Invasive Surgery) procedures havebeen proposed for the planning of orthopedic implant surgeries. Suchsystems do not rely on volumetric patient image data. Instead, thesesystems are image free and use information gatheredintra-operatively—such as centers of rotation of the hip, knee, andankle and visual information like anatomical landmarks—from whichdesired positions of the implants are calculated. These systems provideno planning capabilities before the surgery and navigation is based onthe information that is calculated rather than obtained from thepatient's true anatomy. Structures shown on a screen are alwaysapproximations, such as 3D models obtained from a library of bonesstructures based on the calculations made. Hence, such are less precisecompared to image based orthopedic navigation systems. Furthermore,these systems do not provide any pre-operative planning possibilities,since the calculations and simulations are made intra-operatively.Furthermore, surgical tools are not tracked during the surgical action.Such system is for example disclosed in US application No. 2011/0275957.

WO2011134083 discloses systems and methods for surgical guidance andimage registration, in which three-dimensional image data associatedwith an object or patient, is registered to topological image dataobtained using a surface topology imaging device. The surface topologyimaging device may include fiducial markers, which may be tracked by anoptical position measurement system that also tracks fiducial markers ona movable instrument. The instrument may be registered to thetopological image data, such that the topological image data and themovable instrument are registered to the three-dimensional image data.The system may also co-register images pertaining to a surgical planwith the three-dimensional image data. The fiducial markers may betracked according to surface texture. The system utilizes fiducialmarkers attached to surgical instruments that have a fixed relationshiprelative to an end-effector thereof. Hence, the system becomescomplicated and expensive, since special-purpose surgical instrumentshaving the fiducial markers have to be used with the system. Theposition of the end-effector of the surgical tool is determined andrecorded using a 3D model of the surgical tool, which is imported fromcomputer aided design (CAD) drawings, in which the tool tip is known.Alternatively, the surgical tool can be profiled with a structured lightscanner to obtain its 3D geometry. The tool tip and orientation axis aredetermined from an acquired point cloud. These are time-consumingprocesses for obtaining the positions of the tool tip relative thefiducial markers, which is undesired during surgical action where timeis a scarce resource, not only during the surgical action itself butalso in preparation therefore.

US2009234217A1, US2011251607, and US2007238981A1 disclose variousaspects of navigation systems. However, utilizing various types offiducial markers, they all suffer from at least the same issues as thenavigation system disclosed in WO2011134083, such as in relation to thecalibration of the position of the end-effector or tool-tip.

Hence, an improved surgical navigation method and system and associatedsurgical instruments would be advantageous, and in particular allowingfor improved guidance, precision, increased flexibility,cost-effectiveness, robustness, reliability, efficiency and/or patientsafety would be advantageous.

SUMMARY OF THE INVENTION

Accordingly, embodiments of the present invention preferably seek tomitigate, alleviate or eliminate one or more deficiencies, disadvantagesor issues in the art, such as the above-identified, singly or in anycombination by providing flexible orthopedic surgical guidanceintegrated with an image-based pre-operative plan according to theappended patent claims.

According to a first aspect, a method for computer assisted orthopedicfeedback of at least one surgical object relative a pre-operative plan,wherein the surgical object is moveable relative to a patient structureduring surgery is provided. The pre-operative plan includes a virtualobject, which is the virtual representation of the surgical object, anda virtual structure, which is the virtual representation of the patientstructure. The method comprises providing the pre-operative planincluding planned position and orientation of the virtual objectrelative to of the virtual structure; obtaining the position of thepatient structure based on a surface of the patient structure using asurgical navigation system; obtaining the position of the surgicalobject using the surgical navigation system; registering the patientstructure to the virtual structure, and optionally or additionallyregistering the surgical object to the virtual object; tracking acurrent position and orientation of the surgical object using thesurgical navigation system; and providing feedback of a current positionand orientation of the surgical object relative to the planned positionand orientation of the virtual object based on the tracked currentposition and orientation of the surgical object.

Tracking the current position and orientation of the surgical object maycomprise calibrating the position of an end-effector of the surgicalobject relative a calibration unit within the surgical navigationsystem.

Calibrating the position of the end-effector of the surgical object maycomprise calibrating the position of a navigation unit of the surgicalobject relative a surface with a predetermined position of thecalibration unit.

Calibrating the position of the navigation unit of the surgical objectmay comprise determining the position of a navigation unit of thecalibration unit, the navigation unit having a fixed positionalrelationship relative the surface with a predetermined position.Optionally or additionally calibrating the position of the navigationunit of the surgical object may comprise registering multiple positionsof the navigation unit of the surgical object while it is moved in atleast one plane and the position of the end-effector is substantiallyfixed at the surface with the predetermined position, and determiningthe position of the end-effector based on the registered multiplepositions of the navigation unit of the surgical object.

Providing the feedback may comprise proving at least one of: visualfeedback of current position and orientation of the virtual objectrelative to the planned orientation and position of the virtual objecton a display in response to the tracked current position and orientationof the surgical object; visual indication of the deviation of a currentposition and orientation of the virtual object relative the plannedposition and orientation of the virtual object on a display in responseto the tracked current position and orientation of the surgical object;and visual indication of the deviation of the current position andorientation of the surgical object relative the planned position andorientation of the virtual object in response to the tracked currentposition and orientation of the surgical object, wherein the visualindication is indicated at the surgical object.

The method may comprise tracking the current position and orientation ofthe patient structure, and compensating the position and orientation ofthe virtual object based on the tracked current position and orientationof the patient structure.

Obtaining the position of the surgical object may comprise obtaining theposition and orientation of at least one of a bony anatomy of thepatient, a surgical template having at least one surface with a shapethat is complementary to the shape of the bony anatomy of the patient, asurgical instrument, and an implant for implantation into the patientstructure. Obtaining the position of the patient structure may compriseobtaining the position and orientation of a bony anatomy of the patient.

The method may comprise obtaining the position of the patient structureusing a 3D-6D navigation system having a first accuracy. Additionally oralternatively, the method may comprise obtaining the position of thesurgical object using a 6D navigation system having a second accuracy.The second accuracy may be equivalent or higher than the first accuracy.

Tracking the current position and orientation of the surgical object maycomprise tracking using at least one gyro and at least one accelerometerto generate position and orientation data of the surgical object. Themethod may comprise wirelessly transferring the position and orientationdata of the surgical object from the surgical navigation system to aposition communication hub.

Tracking the current position and orientation of the patient structuremay comprise tracking the position of a navigation unit, using thesurgical navigation system, attached to the patient structure.

Providing the pre-operative plan may comprise: accessing volumetric scandata, wherein the scan data comprises patient structure scan data;converting the patient structure scan data into the virtual structure,which comprises a three dimensional representation of the patientstructure; planning at least one position and orientation of the virtualobject relative to the virtual structure; registering the plannedposition and orientation of the virtual object; and including at leastone of the scan data and the three dimensional model of the virtualstructure together with the planned position and orientation of thevirtual object in the pre-operative plan.

According to a second aspect, a system for computer assisted orthopedicfeedback of at least one surgical object relative a pre-operative planis provided. The surgical object is moveable relative to a patientstructure during surgery. The pre-operative plan includes a virtualobject, which is the virtual representation of the surgical object, anda virtual structure, which is the virtual representation of the patientstructure. The system comprises a position registration unit adapted toobtain at least one position of the patient structure based on a surfacethereof and at least one position of the surgical object; a planningunit adapted to provide the pre-operative plan including plannedposition and orientation of the virtual object relative to the virtualstructure, and to register the patient structure to the virtualstructure, and optionally or additionally registering the surgicalobject to the virtual object; a tracking unit adapted to track a currentposition and orientation of the surgical object; a communication hubadapted to communicate position data from the position registration unitto the planning unit, and from the tracking unit to the planning unit;and a feedback device adapted to provide feedback of the currentposition and orientation of the surgical object relative to the plannedposition and orientation of the virtual object in response to thetracked current position and orientation of the surgical object.

The system may comprise a calibration unit for calibrating the positionof an end-effector of the surgical object relative the calibration unit.

The calibration unit may comprise a surface having a predeterminedposition for receiving the end-effector of the surgical object, andoptionally having a predetermined shape for positioning the end-effectorin a substantially fixed position.

The calibration unit may comprise a navigation unit having a fixedpositional relationship relative the surface with a predeterminedposition. Optionally or additionally the surface with a predeterminedposition has a shape to position the end-effector in at least one planeor position and to allow the surgical object to be freely moveable in atleast one other plane. The position registration unit may be adapted toregister multiple positions of the navigation unit of the surgicalobject as it is moved. The calibration unit may be adapted to determinethe position of the end-effector based on registered multiple positions.

The feedback device may comprise an indicator, which may be integratedwith the surgical object. The indicator may be adapted to provideindication of the deviation of the current position and orientation ofthe surgical object relative the planned position and orientation of thevirtual object. The indicator may comprise a visual indicator, a tactileindicator, and/or an audio indicator.

The feedback device may comprise comprises at least one of: visualindicator adapted to provide, on a display, visual feedback of currentposition and orientation of the virtual object relative to the plannedorientation and position of the virtual object in response to thetracked current position and orientation of the surgical object; visualindicator adapted to provide, on a display, visual indication of thedeviation of the current position and orientation of the virtual objectrelative the planned position and orientation of the virtual object inresponse to the tracked current position and orientation of the surgicalobject; visual indicator, which is integrated with the surgical objectand adapted to provide visual indication of the deviation of the currentposition and orientation of the surgical object relative the plannedposition and orientation of the virtual object.

The tracking unit may be adapted to track the current position andorientation of the patient structure. The tracking unit may additionallyor alternatively be adapted to compensate the position and orientationof the virtual object based on the tracked current position andorientation of the patient structure.

The tracking unit may be adapted to track a surgical object in the formof at least one of a bony anatomy of the patient, a surgical templatehaving at least one surface with a shape that is complementary to theshape of the bony anatomy of the patient, position and orientation of asurgical instrument relative to the patient structure, and an implantfor implantation into the patient structure. The tracking unit may beadapted to track the patient structure in the form of a bony anatomy ofthe patient.

The tracking unit may comprise a navigation unit, such as positionsensor, attachable to the patient structure at a fixed position relativethe patient structure, and a tracking receiver, such as a positionreceiver, for receiving the position of the navigation unit.

The position registration unit may be adapted to obtain the position ofthe patient structure using a 3D-6D navigation system having a firstaccuracy, and additionally or alternatively to obtain the position ofthe surgical object using a 6D navigation system having a secondaccuracy. The second accuracy may be equivalent or higher than the firstaccuracy.

The tracking unit may comprise at least one gyro and at least oneaccelerometer to generate position and orientation data of the surgicalobject or an optical navigation system. The tracking unit may comprise acommunication device adapted to wirelessly transferring the position andorientation data of the surgical object from the tracking unit to theposition communication hub.

The planning unit may be adapted to: access volumetric scan data thatcomprises patient structure scan data; convert the patient structurescan data into the virtual structure, which comprises a threedimensional representation of the patient structure; generate, based onuser interaction, a plan of at least one position and orientation of thevirtual object relative to the virtual structure; register the plannedposition and orientation of the virtual object; and include at least oneof the scan data and the three dimensional model of the virtualstructure together with the planned position and orientation of thevirtual object in the pre-operative plan.

According to a third aspect, a computer program product, executable on aprogrammable device contains instructions in the form of code segments,which when executed, performs the method according to embodiments of theinvention.

According to a fourth aspect, a computer program product is stored on acomputer usable medium, which comprises computer readable program meansfor causing a computer to carry out the various steps of embodiments ofthe method of the invention when executed.

Further embodiments of the invention are defined in the dependentclaims.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps or components but does not preclude thepresence or addition of one or more other features, integers, steps,components or groups thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of which embodiments ofthe invention are capable of will be apparent and elucidated from thefollowing description of embodiments of the present invention, referencebeing made to the accompanying drawings, in which

FIG. 1 is a schematic view of the system according to embodiments of theinvention;

FIG. 2 is a flow chart of an embodiment for computer assisted orthopedicfeedback;

FIG. 3 is a block diagram of an embodiment of a computer system forpreparing a pre-operative plan;

FIG. 4 is a front-view of a display in which a pre-operative plan isillustrated;

FIG. 5 is a perspective view of a surgical template;

FIG. 6 is a flow chart of an embodiment of a method for tracking theposition of a surgical object during surgery and providing feedbackrelative to the pre-operative plan;

FIG. 7 is a block diagram and a schematic view illustrating anembodiment of a navigation system used during a surgical situation;

FIG. 8 is a schematic view of a display illustrating an embodiment ofdisplaying the tracked position and orientation of the surgical objectrelative to the pre-operative plan;

FIG. 9 is a schematic view of a display illustrating another embodimentof displaying the tracked position and orientation of the surgicalobject relative to the pre-operative plan;

FIGS. 10a-10c are perspective views of the system according toembodiments of the invention;

FIGS. 11a-11e are front views of embodiments of calibration units; and

FIG. 12 is a perspective view of an embodiment of a calibration unit.

DESCRIPTION OF EMBODIMENTS

Specific embodiments of the invention will now be described withreference to the accompanying drawings. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art. Theterminology used in the detailed description of the embodimentsillustrated in the accompanying drawings is not intended to be limitingof the invention. In the drawings, like numbers refer to like elements.

The following description focuses on embodiments of the presentinvention applicable for tracking the position of a surgical objectduring surgery, and transforming the position of the surgical objectfrom the surgical theatre into a pre-operative plan of the surgicalprocedure. The pre-operative plan includes a virtual object, which is avirtual representation of the surgical object, and a virtual structure,which is a virtual representation of the patient structure, upon whichthe surgery is to be performed. Embodiments of the invention will bedescribed with regard to orthopedic surgery. However, it will beappreciated that the invention is not limited to this application butmay be applied to many other implant based surgical procedures, such asdentistry, dental surgery, etc., wherein the position of a surgicalobject, such as a drill or a dental implant, is tracked and transformedinto the pre-operative plan. These planning procedures have in commonthat the pre-operative plan may comprise planning the position andorientation of an object that is extrinsic to the patient structure,such as a bony anatomy of the patient.

Embodiments of the invention are aimed at providing feedback of thecurrent position and orientation of the surgical object relative theplanned position and orientation of the virtual object during surgery inthe context of the pre-operative plan. The feedback may be visualized ona display, wherein the virtual object and the virtual structure arerendered. During the course of the surgical procedure, the current oractual position and orientation of the virtual object relative to theposition of the virtual structure will substantially correspond to thecurrent position and orientation of the surgical object relative to theposition of the patient structure. Hence, the actual position andorientation of the surgical object may be displayed relative to thepre-operative plan. Using embodiments of the invention, this may be donein real time. Thus, feedback is provided of the current or actualposition and orientation of the virtual object relative to the plannedposition and orientation of the virtual object. Based on this feedback,the surgeon may be guided to the correct planned position of thesurgical object. Yet, the surgeon can freely move the surgical object.Hence, embodiments of the invention provides guidance for correctpositioning of the surgical object and is at the same time flexiblesince the ultimate decision of the position of the surgical object is inthe hands of the surgeon. Also, feedback may be provided of the currentor actual position and orientation of the virtual structure relative tothe pre-operative plan of the virtual structure.

In embodiments of the invention, the position of the surgical object maybe visually indicated, and plan data for the surgical object which e.g.may comprise a plurality of planned positions and/or orientations of asurgical instrument during various stages of the surgery. The virtualstructure and the corresponding patient structure may be used as thecommon denominator in the pre-operative plan and in reality,respectively. A shape of the surface of the surgical object and/or thepatient structure may be present in the pre-operative plan and duringsurgery. This shape can be used to provide the positional relationshipof the patient structure in reality and the corresponding virtualstructure in the pre-operative plan for the registration, as will bedescribed below. A system and method according to embodiments of theinvention comprise a number of components, data and steps. Embodimentsof the invention will be described below with regard to various areas inorder to structure various components data and steps. It should be notedthat in some embodiments, not all areas are included. Furthermore, someareas and/or sub-areas thereof may form independent embodiments, but maynot be independently covered by the claims. Embodiments of the inventionwill be described with regard to the areas: system overview;pre-operative plan; position registration; tracking; and feedback.Embodiments of various methods for pre-operatively planning a surgicalprocedure is described with regard to various steps, and embodiments ofvarious methods for operating the system according to the inventionduring surgery is described with regard to various steps, some of whichare illustrated in FIGS. 2 and 6.

System Overview

FIG. 1 illustrates an overview of a system for computer assistedorthopedic surgery, according to embodiments of the invention. Thesystem comprises a planning unit 1, at least one position registrationunit 2, at least one tracking unit, a communication hub 4, and afeedback device 5. Using the planning unit 1, a pre-operative plan of asurgery may be made before the surgery commences. The pre-operative planmay be based on volumetric scan data obtained from a medical imagingdevice (not shown), such as a CT (Computer Tomography) or MRI (MagneticResonance Imaging) scanner, to obtain patient specific data. From thevolumetric scan data, the planning unit 1 can segment variousstructures, such as bone, to create a 3D model of a patient structure 7,upon which the surgery is to be performed. The 3D model of the patientstructure 7 provides a virtual representation of the patient structure,which will be referred to in the following as a virtual structure 8.Additionally or alternatively, the virtual structure 8 may comprise 2Dpatient data, such as re-slice of the CT data. Creation of a 3D modelfrom volumetric scan data is generally known and will not be discussedin more detail herein. In the embodiments discussed herein, the patientstructure 7 may comprise a bony anatomical structure of the patient,such as pelvis, femur, tibia, fibula, or spinal cord. Hence, the systemaccording to the invention is suitable for hip surgery, knee surgery,back surgery etc., wherein planning of the procedure may compriseplanning of an extrinsic element is to be introduced in to the patient,such as a hip implant, a knee implant, spinal implant etc.

The planning unit 1 may comprise a computer having software codesegments for providing the pre-operative plan. As such, the planningunit may have one or several input devices 9, such as a keyboard and amouse, and one or several output devices, such as a display 10. Usingthe patient scan data and the virtual structure 8, the pre-operativeplan may be made. The pre-operative plan may comprise planning at leastone position and orientation of surgical object 3 a, 3 b, 3 c relativeto the patient structure 7 during the surgery. In some embodiments, thesurgical object 3 a, 3 b, 3 c comprises an implant, such as a hipimplant or a knee implant. Hence, the pre-operative plan may comprisepositioning and orienting a virtual representation of the surgicalobject, referred to as a virtual object 11, to an optimal position andorientation relative to at least one virtual structure 8. An exampleembodiment would be to position a hip implant relative the femur andorient the head of the hip implant relative to the acetabulum of thepelvis. In relation to a hip replacement, the surgical object, and thusthe virtual object, may comprise both the acetabular cup and the femoralcomponent. Thus the pre-operative plan may comprise planning multiplesurgical objects, 3 a, 3 b, 3 c, such as the acetabular cup and thefemoral component via their virtual representations relative to multiplepatient structures, such as the femur and acetabulum. In the embodimentof FIG. 1, planning of a knee surgery is disclosed, wherein the patientstructure and the virtual representation thereof may comprise multiplestructures, such as the femur tibia, fibula, and/or patella. In thisembodiment, the surgical object is a surgical instrument, and plannedpositions and orientations thereof. Further embodiments of the surgicalobject and the patient structure will be disclosed below. However,common to these embodiments is the surgical object 3 a, 3 b, 3 c, whichis moveable relative to the patient structure 7 during surgery.

The planning unit 1 is adapted to provide the pre-operative planincluding planned position and orientation of the virtual objectrelative to of the virtual structure. Also, the planning unit 1 may beadapted to register the patient structure 7 to the virtual structure 8,and optionally or additionally the surgical object 3 a, 3 b, 3 c to thevirtual object 11, as will be disclosed below.

The system provides feedback of at least one surgical object 3 a, 3 b, 3c relative the pre-operative plan. The pre-operative plan includes thevirtual object 11, which is the virtual representation of the surgicalobject, and a virtual structure 8, which is the virtual representationof the patient structure 7. The virtual object 11 and the virtualstructure 8 may be represented as 3D objects, such as 3D surfaceobjects. Hence the planning unit 1 may be a 3D planning unit.

The position registration unit 2 is according to embodiments of theinvention adapted to obtain at least one position of the patientstructure 7. The position registration unit 2 may operate without anyfiduciary markers present in the scan data as well as during surgery.Hence, the patient does not have to go through any operation to placethe fiduciary markers before the surgery. Instead, the positionregistration unit 2 may operate based on the surface of the patientstructure, such as the shape thereof, positions of the surface within acoordinate system of the position registration unit 2, etc., as will bediscussed further below. The position registration unit 2 may also beadapted to register the position and orientation of the surgical object3 a, 3 b, 3 c.

A tracking unit 12 a, 12 b, 12 c, which may be attached to the surgicalobject 3 a, 3 b, 3 c, is adapted to track a current position andorientation of the surgical object 3 a, 3 b, 3 c within a coordinatesystem and thus relative to the patient structure when they are providedwithin the same coordinate system or coordinate systems that areregistered. The communication hub 4 is adapted to communicate positiondata from the position registration unit 2 to the planning unit 1, andposition and orientation data from the tracking unit 12 a, 12 b, 12 c tothe planning unit 1. Hence, the position of the patient structure 7 canbe registered by the position registration unit 2 and relayed to theplanning unit 1, and registered to the virtual structure 11. Similarly,the position of the surgical object 3 a, 3 b, 3 c can be registered,such as by the registration unit 2 or via docketing station as will bedisclosed below, and its position and orientation continuously trackedby the tracking unit 12 a, 12 b, 12 c, and relayed back to the planningunit 1 via the communication hub 4. Furthermore, in some embodiments,the position registration unit 2 is adapted to dynamically update theposition and orientation of the patient structure 7, i.e. dynamicallyreference the patient structure 7 to the virtual structure 8. Hence, thecommunication hub 4 communicates data to and from the various units inthe system. The planning unit 1 may update the position of the virtualobject 11 relative the virtual structure 8 based on the tracked positionand orientation of the surgical object 3 a, 3 b, 3 c in the coordinatesystem of the position registration unit 2 or the patient depending onhow the system is set up. Hence, the planning unit 1 may dynamicallyreference the surgical object 3 a, 3 b, 3 c, to a virtual representationof the surgical object and the virtual structure.

In embodiments of the invention, the feedback device 5 is adapted toprovide feedback of the current position and orientation of the surgicalobject 3 a, 3 b, 3 c relative to the planned position and orientation ofthe virtual object 11 in response to the tracked current position andorientation of the surgical object 3 a, 3 b, 3 c. In some embodiments,the feedback may be provided by a feedback device, such as an indicator,for example a visual indicator, a tactile indicator, or an audioindicator. A visual indicator may e.g. comprise a display, a lightemitter, such as one or several LEDs, etc. In the embodiment of FIG. 1,the feedback device 5 is a display of the planning unit 1. Hence, thedisplay may render the virtual structure 8, a representation of thevirtual object 11 in its planned position(s) and orientation(s) relativethe virtual structure 8, and a representation of the current positionand orientation of the surgical object 3 a, 3 b, 3 c relative to thepatient structure 7. The representation of the current position andorientation of the surgical object 3 a, 3 b, 3 c relative to the patientstructure 7 may e.g. be provided by a virtual 3D model of the surgicalobject 3 a, 3 b, 3 c. Hence, the visual indicator may be adapted toprovide visual feedback of current position and orientation of thevirtual object relative to the planned orientation and position of thevirtual object based on the tracked current position and orientation ofthe surgical object. This may e.g. be provided via a display. The visualindicator may be provided at the surgical object, such as integratedtherewith, for example within a single chassis of the surgical object.Alternatively or additionally, the visual indicator may be adapted toprovide visual indication of the deviation of the current position andorientation of the virtual object relative the planned position andorientation of the virtual object on a screen, and thus between thecurrent position and orientation of the surgical object and its plannedposition and orientation. This may be provided based on or in responseto the tracked current position and orientation of the surgical object.Some embodiments may also comprise a visual indicator adapted to providevisual indication of the deviation of the current position andorientation of the surgical object relative the planned position andorientation of the virtual object, such as via a visual indicatorintegrated with the surgical object. For example, a multi-colour LED mayindicate the deviation from one or several positions and orientations,such as red indicating >50 mm from planned position and orientation,yellow indicating the range 49 mm< >10 mm from planned position andorientation, and green indicating <10 mm from planned position andorientation. Alternatively, the ranges may be indicated using a singlecolour flashing LED, with different flashing pattern depending on thedeviation. In still other embodiments, the feedback device 5 may beacoustic, wherein the pitch, type of signal, etc. of the acoustic signalwould indicate the ranges. An acoustic feedback, such as by an acousticfeedback device, may complement or replace the other embodiments forproviding feedback. The visual feedback may comprise a cone ofacceptance provided via the feedback device 5 in association with thevirtual 3D model of the surgical object 3 a, 3 b, 3 c.

FIG. 2 illustrates embodiments of a method for computer assistedorthopedic feedback of at least one surgical object 3 a, 3 b, 3 crelative a pre-operative plan. In step 100, the pre-operative planincluding planned position and orientation of the virtual objectrelative to the virtual structure is provided, such as using theplanning unit 1. In step 110, the position of the patient structure isobtained, which may be based on a surface of the patient structure, suchas using the position registration unit 2. In step 120, the position ofthe surgical object 3 a, 3 b, 3 c is obtained, such as using theposition registration unit 2 or a docketing station to track theposition and orientation of the surgical object 3 a, 3 b, 3 c. In step130, the patient structure 7 is registered to the virtual structure 8.The surgical object 3 a, 3 b, 3 c may be registered to the virtualobject 11. Alternatively or additionally, the surgical object may becalibrated for tracking its position relative the virtual structureand/or planned positions of the surgical structure i.e. plannedpositions of the virtual structure relative actual positions of thevirtual structure. In some embodiments, the surgical object 3 a, 3 b, 3c is registered to the virtual object 11 and/or calibrated prior to thesurgical procedure commences, and thus prior to registration of thepatient structure 7. In step 140, the current position and orientationof the surgical object 3 a, 3 b, 3 c is tracked. When the surgicalobject 3 a, 3 b, 3 c and the patient structure 7 are located in the samecoordinate system, or in coordinate systems that are referenced,position and orientation of the surgical object will thus tracked therelative to the patient structure 7. In step 150, feedback of a currentposition and orientation of the surgical object relative to the plannedposition and orientation of the virtual object is provided based on thetracked current position and orientation of the surgical object. Thefeedback may be provided as discussed above with regard to the feedbackdevice 5.

In some embodiments, step 140 comprises tracking the current positionand orientation of the patient structure, and compensating the currentposition and orientation of the virtual object based on the trackedcurrent position and orientation of the patient structure. This may e.g.be provided if the coordinate system is fixed to the patient structure,and the position and orientation of the surgical object is trackedwithin that coordinate system. Dynamic referencing may also be provided,wherein the position of the patient structure 7 is dynamically tracked.

Pre-Operative Plan

Before the surgery commences, planning data from the pre-operative planis provided. The planning data includes patient structure plan data, andsurgical object plan data, such as the virtual representations thereof.This may be provided in a first coordinate system, i.e. the coordinatesystem of the planning unit 1. The virtual object 11 and the virtualstructure 8 may have a fixed positional relationship within the firstcoordinate system when the planning is completed.

The pre-operative plan may comprise a number of steps in order to reachthe position and orientation data for the virtual object 11. This maycomprise accessing volumetric scan data that comprises patient structurescan data; converting the patient structure scan data into the virtualstructure 8, which may comprise a three dimensional representation ofthe patient structure 7; generating, based on user interaction, a planof at least one position and orientation of the virtual object 11relative to the virtual structure 8; registering the planned positionand orientation of the virtual object 11; and including at least one ofthe scan data and the three dimensional model of the virtual structure 8together with the planned position and orientation of the virtual object11 in the pre-operative plan. If the scan data is included together withthe planned position and orientation of the virtual object 11 duringplanning, the virtual structure may be recreated in the planning unit 1before surgery. Hence, the planning unit 1 may be a separate unit from aplanning station upon which the pre-operative plan was made. Still, thesurgeon may have access to the same data as during the planning, such asthe 3D model of the patient structure, scan data, such as CT or MRI datathat can be re-sliced during surgery to provide further information tothe surgeon. Alternatively, the virtual structure is included togetherwith the planned position and orientation of the virtual object. Hence,in some embodiments, only the virtual object 11 and virtual structure 8are available during the surgery. This may also be provided in differentwindows of the display, in which the pre-operative plan and feedback tothe surgeon during surgery is provided.

In some embodiments, the pre-operative plan comprises planning a cut ofa patient structure, such as to separate a femur head from the femur fora hip implant surgery. In this context, it may be desired that the femurhas a certain position and orientation relative to the pelvis or aportion thereof, such as the acetabulum. Hence, in this context, thesurgical object may comprise at least one bony anatomy of the patient.Furthermore, the surgical plan may comprise planning of a surgicaltemplate for guiding a surgical procedure, such as a cut of the femurhead. In this context, the surgical object may comprise a surgicaltemplate having at least one surface with a shape that conforms to theshape of the bony anatomy of the patient. For hip surgery, multiplepatient structures and/or surgical objects may be provided, such as abony anatomy and a surgical template. Additionally or alternatively, thesurgical object may comprise a surgical instrument and its position andorientation relative to the patient structure at one or severalinstances during the procedure. This may e.g. be provided to give visualindications of cuts, drilling operations, etc. such that the surgeon isvisually guided to an optimal and pre-planned path for the instrument.However, the actual movement of the instrument is still completely inthe hands of the surgeon, who is fully in control of the surgery. Theinstrument may be a hand-held surgical instrument. Furthermore, thesurgical object may comprise an implant for implantation into thepatient structure, such as a hip implant including a femur component,and optionally also an acetabular cup.

Generating scan data of a patient is generally known. The scan data maycomprise DICOM data obtained from, for example a medical imagingscanner, such as a CT scanner, MRI scanner, or an X-ray scanner. Thescan data may be supplied in one or multiple files. The scan datacomprises a 3D volume of data out of which 2D slices of information canbe generated during planning. Hence, the surgeon can virtually cutthrough the anatomy of the surgical object in order to plan position andorientation of the surgical object 3 a, 3 b, 3 c, such as one ormultiple positions and orientations of a surgical instrument, positionsand orientations of implant components, and positions and orientationsof surgical templates.

FIG. 3 illustrates a computer system 20, in which the scan data may beimported. The computer system may also be used during surgery as theplanning unit 1, wherein the position data of the surgical object mayalso be accessed. Alternatively, a separate planning unit 1 is providedduring planning, wherein the computer system 20 used during planningdoes not need capability to access the current position data of thesurgical object. The computer system 20 comprises a CPU or dataprocessing unit 21, one or several memories 22, a communication unit 23,a reading unit 24 for reading the scan data, an input device 25, such asa mouse and/or a keyboard, and a feedback device or an output unit 26,such as a display. Furthermore, the computer system 20 may comprisecomputer software for performing a pre-operative plan. The computersoftware may comprise a CAD system, wherein the scan data can berendered, such as a 3D model of the surgical object, and/or 2D slices oforiginal scan data, such as MRI or CT data. The 3D model of the surgicalobject and the 2D scan data may also be rendered at the same time and bepartially overlaid in order to increase the information. The CAD systemmay comprise a general purpose CAD system, such as 3ds Max fromAutodesk®.

Once the scan data has been imported, a 3D model of the surgical object11 can be provided. The 3D model may e.g. be a 3D surface model or apoint cloud created using a 3D graphics technology.

FIG. 4 illustrates an embodiment of planning a surgical procedure andproviding a pre-operative plan. When accessing the scan data, the scandata may comprise patient structure scan data. The patient structurescan data may be converted into the virtual structure 30, which is thevirtual representation of the patient structure. At least one positionand orientation of the virtual object relative to the virtual structure30 is planned for the surgical procedure. In some embodiments, multiplepositions and/or orientations of the virtual object relative to thevirtual structure are planned. Furthermore, positions and/ororientations for multiple virtual objects may be planned, for example ifdifferent surgical objects are used during the procedure.

In some embodiments, planned positions and orientations of the virtualobject may form the positions and orientations of one or several pathsof the virtual object. In the embodiment of FIG. 4, a first path 40 anda second path 41 are illustrated. The path 40, 41 may e.g. be formed byan entry position 42 and an end position 43, which may be indicationsfor entry and end, respectively, positions of an end-effector of thesurgical object, such as the entry and end positions of a drill, such asthe tip thereof. The path may then comprise a straight line between theentry position 42 and the end position 43, which inherently also mayprovide the orientation of the path 40, 41. The straight line does notnecessarily need to be registered, but can be generated when needed asthe entry position 42 and the end position 43 are enough information togenerate a straight path. If the path is curved, one or severaladditional positions between the entry position 42 and the end position43 may be marked and registered. A line may then be generated betweenany two positions, preferably two neighboring positions. In otherembodiments, a single position of the surgical instrument is planned,such as an entry position 42 or an end position 43. In otherembodiments, the virtual object is a 3D object for indicating a regionfor harvesting bone, such as for insertion of a femur component oracetabular cup, for example a virtual representation of the femurcomponent and/or acetabular cup.

In the embodiment of FIG. 4, a knee surgery is illustrated. Surgicalobjects are provided in the form of information for a path for asurgical instrument, such as a surgical drill. Optionally, thepre-operative plan may also comprise virtually positioning and orientingan implant for the knee surgery. The first path 40 has been planned. Thefirst path 40 has been planned by indicating with an object the entryposition 42 and the end position 43. The first path 40 is in thisembodiment a straight line between the entry position 42 and the endposition 43. In this embodiment, the second path 41 has also beenplanned. The first path 40 has been generated by generating a line usingthe input device 25. Then, the line has been positioned, again using theinput device 25, such that the second path 41 passes through the entryposition 42. Hence, two or more paths may share one or several plannedpositions and/or orientations, such as an entry position 42 and/or anend position 43 of the surgical instrument.

In other embodiments, different positions of a surgical template 50relative to other structures, such as relative to a bony anatomicalstructure, are planned. FIG. 5 illustrates an embodiment of the surgicaltemplate 50. The surgical template 50 is a multi part 51, 52 surgicaltemplate, that has been planned to facilitate assembly from a firstassembly direction 53 and a second assembly direction 54 of the surgicaltemplate 50. During surgery, such as when the head of the femur 55 is tobe cut for a hip surgery, the position of the surgical template 50 maybe planned to have a particular position and/or orientation relative atleast a portion of the pelvis (not shown), and/or a portion of thefemur. Hence, the position and orientation of the surgical template 50relative the bony anatomy of the patient at the time when a portion ofthe femur is cut may be planned. In another example, during kneesurgery, the surgical template (not illustrated) may have a firstposition and orientation relative to the tibia and/or fibia during afirst stage of the surgery, and a second position and orientationrelative to the tibia and/or fibia during a second stage of the surgery(which may also include positioning and orienting multiple surgicaltemplate for this purpose). In such a situation, the planning softwaremay comprise simulation capabilities, wherein movement of differentstructures of the 3D model of the patient can be simulated. Hence, for afirst stage of the surgery, a first positions of the surgical template50, and/or a first position of a surgical instrument, relative thevirtual structure or structures can be planned, wherein the differentvirtual objects have a first positional relationship relative to thevirtual structure. Movement of a virtual structure is simulated suchthat the different parts of the virtual structure have a secondpositional and orientation relationship. Then, a second position andorientation of the surgical template, and/or a second position andorientation of the surgical instrument, can be planned, such as a secondpath and/or a second position and orientation of the surgical template50.

In other embodiments, a dental procedure may be planned. For example,the position of a dental implant in the jawbone may be planned. Theposition and orientation of the dental implant may, e.g., be planned bypositioning a virtual object representing the dental implant. In itsplanned position, the head of the dental implant marks the entryposition for a drill, and the tip of the dental implant marks the endposition for the drill. The path is a straight path between the entryposition and end position. Furthermore, the distance between the entryposition and the end position, and/or the type and size of dentalimplant, may indicate the length and/or diameter of a correspondingsurgical object, which in this embodiment may comprise a drill. Thedental implant may comprise a screw type dental implant. Similar typesof procedures may also be planned for other straight implants similar todental implants, such as an implant for spinal fusion.

Once the planning of the surgical procedure is complete, thepre-operative plan is provided 100. The pre-operative plan may comprisethe scan data with the planned positions and orientations for thesurgical object in a first coordinate system in a fixed relationship.Alternatively or additionally, the pre-operative plan may comprises the3D model of the patient structure 30 together with the planned positionsfor the surgical object in the first coordinate system in a fixedrelationship. Any of these data sets is referred to as the pre-operativeplan.

The pre-operative plan may be provided at the time of surgery. Duringsurgery, the computer system 20 may be provided, wherein the virtualstructure representing the patient structure 30 can be recreated fromthe scan data. Alternatively, the virtual structure 30 representing thepatient structure and the planned positions and orientations of thevirtual object are provided in the same coordinate system in theplanning data, wherein optionally also the scan data may be provided.

The computer system 20 may comprise the first coordinate system, inwhich the virtual structure and the planned positions and orientationsof the virtual object in relation thereto are provided, such as theplanned paths 40,41. For example, the first coordinate system may be thecoordinate system of a CAD software where the scan data, virtualstructure, and the virtual object are present or provided.

Included in the pre-operative plan may also be supplied surgical objectinformation, such as concerning type, and/or size, such as length and/ordiameter, of the surgical object. For example, the surgical object maycomprise a drill, such as a bone drill for orthopedic or dentaldrilling. Hence the surgical object type is drill. If various sizes forthe drill may be planned, the size of the drill may be included in theplanning data. In other embodiments, the surgical object is a mill, asaw, etc. Hence, each virtual object, such as a planned path and/orposition thereof, may be associated with surgical object information.

According to embodiments of the invention, surgical objects may e.g.comprise a surgical template, a drill, a saw, a cutter, and/or a dentalhand piece.

Position Registration

According to embodiments of the invention, position registration unit 2is a surface based position registration unit. Surface-basedregistration is highly accurate and reliable, and does not require anysurgical procedure prior to the surgery of the patient structure. Usingthis technique for registration, a cloud of surface points on thepatient structure may be collected using a tracked probe. The positionsfrom the surface of the bone having a unique shape are then used tomatch the pre-operative plan with the position of the patient in theoperating room. Hence, the patient structure may be registered to thevirtual structure using this technology. Furthermore, an initialposition of the surgical object may be obtained using this technology,and then registered to the virtual object. Any deviation between theactual position of the surgical object and the planned position of thevirtual object may be indicated via the feedback device 5.

The planning unit 1 may be adapted to import the point cloud, such as inany of the file formats iges, step, and stl. Furthermore, the surfacedata of the patient structure may also be provided as volumetric data,such as voxel data. Furthermore, the planning unit may be adapted tomake coordinate transformations, Union cross sections, and Booleanoperations. Furthermore, the planning unit may be adapted to providematching operations, such as surface or volume matching.

The position registration unit 2 may be adapted to obtain the positionof the patient structure using a first navigation system such as a 3D-6Dnavigation system having a first accuracy. If the coordinate systemduring the operation is affixed to the patient structure, it is onlynecessary to use a 3D navigation system to register the position of thepatient structure to capture the spatial location in three degrees offreedom. If the coordinate system is not affixed to the patientstructure, also the orientation of the patient structure in thecoordinate system may be obtained, whereby a 6D navigation system may beused for the additional degrees of freedom roll, yaw, pith. Furthermore,the position registration unit 2 may be adapted to obtain the positionand orientation of the surgical object using a second navigation system,such as a 6D navigation system. The navigation system to obtain theposition of the patient structure may be the same or different than thenavigation system to obtain the position and orientation of the surgicalobject. The second navigation system may have a second accuracy, whichis equivalent or higher than the accuracy of the first navigationsystem. Hence, it will be possible to track the position and theorientation of the surgical object relative to the patient structure.The first accuracy is preferably better than a mean deviation of 0.2 mm,even more preferably better than 0.1 mm.

The navigation systems may e.g. be an optical navigation system. In oneembodiment, the navigation system is an image guided navigation systemthat comprises a tracked probe with embedded light sources, such asLEDs, providing a navigation unit as will be further discussed below.Positions on the surface of the patient structure may be registered andenough surface points obtained for the registration. A system forobtaining the shape or point cloud is e.g. disclosed in WO91/16598,which is incorporated herein by reference for all purposes. Point bypoint measurements may also be made using a touch probe to collectspatial positions of a surface for a point cloud, such as is disclosedin U.S. Pat. No. 5,440,392, which is incorporated herein by referencefor all purposes. Another embodiment of an optical navigation system isdisclosed in U.S. Pat. No. 6,166,809, which is incorporated herein byreference for all purposes, with which both position and orientation maybe obtained.

According to embodiments of the invention, optical navigation systemsmay be used to obtain the position of the patient structure. Whenpositions from the surface of the patient structure has been obtained,the point cloud may be used to register the patient structure to thevirtual structure. The registered information about the surface iscompared with the virtual structure, such as in the form of a 3D surfacemodel. A registration matrix between the two surfaces may be computedusing iterative closest point (ICP) algorithm. After the transformation,the positional relationship between the patient structure and virtualstructure is obtained. Registration of the surgical object relative thevirtual object may be made in the same way as the patient structurerelative the virtual structure. The registration matrix may comprise atransformation matrix including translation and rotation identities,such as x, y, z translation identities and roll, pitch, yaw identities.

In some embodiments, the position registration unit comprises a sensorand a receiver. In some embodiments the position registration unit is anoptical tracking system, wherein the sensor may comprise and passive oractive sensor, such as a fiducial marker and/or a LED, and the receiveris an optical receiver, such as one or many cameras. In otherembodiments, the position registration unit comprises a transmitter andposition determination unit, wherein the position in space relative aknown location is registered and transmitted to a receiver in thesystem. The sensors, transmitters, position determination units arecollectively referred to as navigation unit herein. Tracking unit 12 a,12 b, 12 c may each comprise a navigation unit, such as one or severalsensors, transmitters, and/or position determination units, based on thetechnologies as described herein, such as optical components, MEMS,gyros, accelerometers, etc.

In some embodiments, the surgical object comprises a detachablenavigation unit, such as tracking unit 12 a, 12 b, 12 c. The navigationunit may be attached and detached to the to the surgical object in asingle repetitive position. The detachable navigation unit may beconnected to the surgical object via a connection interface or referencesurface, which may have one or several projections and recesses such thenavigation unit fits to a connection interface or reference surface ofthe surgical object having a complementary shape. Hence, the detachablenavigation unit fits to the surgical object only in a singe pre-definedposition. Furthermore, the navigation unit may comprise informationabout the surgical object to which it is attached, such as a position ofan end effector of the surgical object, e.g. the tip of a drill ormilling tool, relative the connection interface of the surgical object.Hence, by determining the position and orientation of the connectioninterface of the surgical object or the position and orientation of thenavigation unit, the position and orientation of the surgical object maybe obtained. This information may be transferred to the communicationhub 4, such as via a wireless communication device, such as using WiFior Bluetooth® technology. In some embodiments, the navigation unit to beattached to the surgical object may be based on the optical navigationsystems referred to above.

The registration of the acquired positions from the patient structureand/or the surgical object may be made using, e.g. a best-fitregistration, surface fit registration etc. Algorithms for this purposeare generally known and will not be further disclosed herein. However,it should be noticed that it is important that the surface positions areobtained from an area represented in the virtual structure. For example,if the patient scan is made using CT, the surface should be a bonesurface and not a cartilage surface, which is normally not the surfacewhich forms the basis for the 3D model, but rather the bone surface.However, if the patient scan is made using MRI, the surface from whichpositions are captured may comprise a cartilage surface. However, if thepatient scan comprise both types of scan data, this may not be an issue.

FIG. 6 illustrates a method for tracking the position of the surgicalobject illustrated as a surgical instrument using a surgical navigationsystem 70 illustrated in FIG. 7. In step 200, the surgical navigationsystem 70 is provided. In step 210, the pre-operative plan and plannedposition and orientation of the virtual object relative to of thevirtual structure are provided. The surgical navigation system 70 isprovided within the surgical theatre or operating room. The surgicalnavigation system 70 comprises a calibration unit 71 and is associatedwith or comprises a second coordinate system. Hence, the calibrationunit 71 has a fixed position within the second coordinate system when itis used for calibrating various instruments and devices as will bedescribed below. The calibration unit 71 may be provided as a docketingstation, within which the origin of the second coordinate system may beprovided. The calibration unit 71 is provided to calibrate the positionof the surgical object 77, or the navigation unit thereof, a detachablenavigation unit as discussed above, and/or other tools, as will bedescribed below, within the second coordinate system. In more detail,each surgical object 77 may comprise a navigation unit 72 a, 72 b.Before the surgery commences, the position of the navigation unit 72 a,72 b may be calibrated, such as illustrated in step 220, i.e. itsposition and orientation within the operating room may be registered.The position and orientation of the navigation unit 72 a, 72 b relativeto the surgical object 77, such as an end-effector, may be known orcalculated. For example, the position and orientation of the navigationunit 72 a, 72 b may have a fixed position and orientation relative anend effector of the surgical object 77, or may be calculated as will befurther described below. After calibration of the position andorientation of the navigation unit 72 a, 72 b is made, the position andorientation of the navigation unit 72 a, 72 b, and hence the position ofthe surgical object 77, may be tracked in space as will be discussed inmore detail below.

Furthermore, the surgical navigation system 70 comprises thecommunication hub. The communication hub may comprise first acommunication unit 73 a connected to a data processing unit 74. The dataprocessing unit 74 may be connected to the planning unit 75 that may bedesigned similar to computer system 10 described in relation to FIG. 3.The surgical object 77 may comprise a second communication unit 73 b,for communicating the tracked position and orientation of the surgicalobject to the data processing unit 74. The communication system may e.g.be a short-range wireless communication system, such as a Bluetooth® ora WiFi communication system.

The surgical navigation system 70 may be an inertial navigation system(INS), which continuously can calculate the position, orientation, andvelocity (direction and speed of movement) in 3D space of the surgicalobject and/or a position registration unit 80 (FIG. 7), such as thetracked probe. Hence, once the position and orientation of the surgicalobject 77 and/or the position registration unit 80 has been calculated,the direction and speed of movement can be tracked. For this purpose thenavigation unit 72 a, 72 b may comprise angular accelerometers tomeasure how the surgical instrument and/or the position registrationdevice is oriented in space. There may be one angular accelerometer foreach axis, i.e. roll, yaw and pitch. Furthermore, the navigation unit 72a, 72 b may comprise a linear accelerometer for each axis, up & down,left & right, and forward & back to track the spatial position. Togetherthe six degrees of freedom can be tracked. The data processing unit 74can be arranged to calculate the current position and orientation of thesurgical object 77 and/or the position registration unit 80.Alternatively, a data processing unit is integrated together with thenavigation unit 72 a, 72 b and integrated with the surgical object 77and/or the position registration unit 80.

In some embodiments, the navigation unit 72 a, 72 b comprises aninertial measurement unit (IMI) that uses a combination ofaccelerometers and gyroscopes to report the surgical object's and/or theposition registration unit's velocity, orientation, and gravital forces.In some embodiments the IMI is a wireless IMI (WIMU). The IMI sensorallows the data processing unit 74 to compute the position andorientation of the surgical object and/or the position registration unitvia e.g. dead reckoning calculations.

In some embodiments, the navigation unit 72 a, 72 b is built on MicroElectro-Mechanical System (MEMS) technology. Such a navigation unit 72a, 72 b may comprise a multi-axis gyro module with up to three axes ofhighly accurate MEMS gyros and/or accelerometers. Such modules are forexample available from Sensonor, Norway. For example, the STIM210 moduleprovides sufficient accuracy for use in embodiments of the surgicalnavigation system according to the invention. Alternatively, MEMSinertial motion sensors for integration with the system according toembodiments of the invention are available from IMEGO AB, Sweden.

Designing an INS is for example described in DESIGN OF AN INERTIALNAVIGATION UNIT USING MEMS SENSORS, by Maksim Eskin, Project Advisor:Bruce Land Degree, Date: January 2006, which is incorporated herein byreference for all purposes.

Registration

As is illustrated in FIG. 7 the navigation system 70 may comprise theposition registration unit 80. The position registration unit 80 isconfigured to register positions on the surface of the patientstructure. In some embodiments, the position registration unit 80 iscompletely separate form the surgical object, such as illustrated inFIG. 7. In other embodiments, the position registration unit 80 isprovided together with the surgical object 77, such as within the samechassis.

The position registration unit 80 comprises a navigation unit 72 b, anda communication unit 73 c, configured as the navigation unit 72 a andthe communication unit 73 b of the surgical object 77 disclosed above.Hence, the position of the position registration unit 80 within thesecond coordinate system may be tracked and communicated to the dataprocessing unit 74. If the position registration unit 80 and thesurgical instrument 77 are provided as a single unit, they may share thesame navigation unit and communication unit.

The position registration unit 80 comprises a position registrationprobe 76. Hence, the position registration unit may form a trackedprobe. The position registration probe 76 is configured to determine andregister positions of patient structure within the second coordinatesystem, such as to capture a point cloud, illustrated in step 240. Thepositions of patient structure can be determined by their coordinateswithin the coordinate system. The positions of the of the patientstructure surface can be registered using e.g. projection technology,wherein a laser patter is projected by the position registration probe76 onto the physical landmark, and whereby the shape of the pattern whenprojected can be recognized and the location of the surface positionrelative the position registration unit 76 may be determined. In otherembodiments, the position registration unit 76, and or the surgicalinstrument, comprises computer vision technology and uses image analysisfor identifying the positions of the surface of the patient structure.The image data may e.g. be acquired using a camera taking multipleimages, a video camera, or multi dimensional data from a medicalscanner. In still other embodiments, the position registration probe 76is a holographic position determination unit. Such a unit may e.g. beprovided using conoscopic holography, which may use a holographictechnique based on light propagation effects in uniaxial crystals. Suchtechnology has previously been used in 3D scanners for scanning 3Dobjects in order to record the shape thereof, but has previously notbeen used in a navigation system for registering the position of apatient structure. The position registration probe 76 has a fixed knownposition relative the navigation unit 72 b. Hence, tracking the positionof the navigation unit 72 b also tracks the position of the positionregistration probe 76. By registering the position of the patientstructure surface relative the position registration unit 76, theformer's coordinates may be determined. In still other embodiments, theposition registration probe 76 comprises optical registrationtechnology, such as discussed above.

Providing the position registration unit 80 integral with the surgicalobject 77 has the benefit that the position of the patient structure canbe registered in real time during the course of the surgical procedure.Hence, if the patient structure unexpectedly moves during the surgery,this is detected and fed back to the data processing unit 74. Hence, thecombined surgical object and position registration unit comprises aposition registration unit, a navigation unit, and a communication unitfor wireless communication. Thereby, the tool is very flexible, and itsposition in space can be tracked without being limited by any mechanicalarrangement, as is the case in robotic surgical systems.

According to embodiments of the method of the invention, the position ofthe patient structure is registered within the second coordinate systemby means of the surface thereof. The patient structure surface hascorresponding position relative to the surgical object as the surface ofthe virtual structure relative to the virtual object in thepre-operative plan.

Registering the position of the patient structure by means of thesurface thereof within the second coordinate system may comprisecalibrating the position registration unit 80 within the surgicalnavigation system by docketing the navigation unit 72 b of the positionregistration unit to a known position of the calibration unit 71 in thesurgical navigation system 70. This may e.g. be done in the same way ascalibrating the surgical tool, as has been described above. Then,movement of the position registration unit in the second coordinatesystem is tracked using the navigation unit 72 b of the positionregistration unit 80. Positional information of the surface of thepatient structure in the surgical navigation system, i.e. in the secondcoordinate system is registered using the position registration unit 80,such as the position registration probe 76 thereof. The registeredpositional information may be communicated to the data processing unit74. The registration of the patient structure to the virtual structuremay be made as discussed above, wherein the coordinate system of thepre-operative plan and the coordinate system of the patient ornavigation system are registered.

In still alternative embodiments, the surface information of the patientstructure is provided using a volumetric scanner, from which the surfaceinformational may be segmented. Then, matching to the virtual structuremay be performed as discussed above.

Tracking

FIGS. 7 and 8 illustrate the tracking, also referred to as dynamicreferencing, of the position and orientation of the surgical object 77,also illustrated by step 250 of FIG. 6. In order to provide theinformation concerning the tracked position and orientation of thesurgical object into the pre-operative plan, the first coordinate systemand the second coordinate system are aligned in step 230. Hence, aposition in space in the second coordinate system is translated into anindication of the position in the first coordinate system, such asillustrated by step 260 of FIG. 6. The first coordinate system and thesecond coordinate system may be aligned by generating a relationshipbetween the position information of the surface of the patient structurewithin the first coordinate system and the position of the correspondingvirtual structure within the second coordinate system. In the firstcoordinate system, the position and optionally orientation of thevirtual structure is known or can be calculated from the planning data.The position and optionally orientation of the corresponding patientstructure are known from the registration process 220 described above.Hence, using this knowledge, it is possible to set up a coordinatetransformation matrix, whereby the first coordinate system and thesecond coordinate system may be aligned. Hence, the first coordinatesystem and the second coordinate system may be aligned making use of thepatient structure and the corresponding virtual structure. Using thecoordinate transformation matrix, a position and orientation of apatient structure or surgical object in the second coordinate system canbe translated into an indication of the position and orientation in thefirst coordinate system. Setting up a coordinate transformation matrixin generally known, and is e.g. described in Global Positioning Systems,Inertial Navigation, and Integration, Mohinder S. Grewal, Lawrence R.Weill, Angus P. Andrews Copyright 5 2001 John Wiley & Sons, Inc.PrintISBN0-471-35032-X ElectronicISBN0-471-20071-9, AppendixC—Coordinate Transformations, which is incorporated herein by referencefor all purposes. Hence, translating a position and orientation in thesecond coordinate system into an indication of that position in thefirst coordinate system may comprises translating using the relationshipbetween the position of the surface of the virtual structure within thefirst coordinate system and the position of the corresponding patientstructure within the second coordinate system, which may be done usingthe coordinate transformation matrix. This is different from roboticsurgical systems, wherein the patient is registered into the coordinatesystem of the robot, which in turn has a fixed relationship to thecoordinate system of the planning, since the robotic arms are fixed to aframe having an origin that is already aligned with the origin of theplanning system. According to embodiments, the surgical object has nomechanical connection to the origin of the second coordinate system andcan be freely moved, the coordinate systems first has to be alignedbefore feedback of the movement can be indicated in relation to theplanning data, such as illustrated by step 260 of FIG. 6. However, thisprovides superior flexibility of movement of the surgical tool duringsurgery since it can be moved in all degrees of freedom without anyrestrictions by mechanical linkage or wires. Furthermore, additionalguidance is provided to the surgeon by the feedback of the position andorientation of the surgical object relative to the planned position andorientation of the corresponding virtual object in the pre-operativeplan. Also, tracking of movement of surgical templates etc. is notpossible in the robotic systems, but is according to embodiments of theinvention. For such tracking, a connection interface may be includedinto the planning, which may have the same shape as the connectioninterface described above with regard to the detachable navigation unit.Hence, the position of the connection interface may be planned relativeto the virtual object and/or the virtual structure, such that it doesnot interfere with the surgical procedure. Hence, when the connectioninterface is located in its planned position and orientation duringsurgery, the planned position and orientation of the surgical templaterelative the virtual object and thus the patient structure has beenobtained.

When the first and the second coordinate systems have been aligned, theposition and orientation of at least one surgical object within thesecond coordinate system can be tracked in step 220 using the surgicalnavigation system. The tracked position and orientation of the surgicalobject within the second coordinate system can be translated intopositional and orientation information in the first coordinate system.The translation may e.g. be made by the data processing unit 74;alternatively, the translation may be made by a processing unit in thecomputer system 10 wherein the planning was made or a similar systemsuch as planning unit 75. Basically, since the data concerning themovement can be freely communicated, the actual translation of themovement in the second coordinate system can be made depending oncomputational efficiency and/or depending on the type of positionalinformation to be indicated in the first coordinate system. The positionand orientation of the surgical object within the second coordinatesystem can be calibrated, as has been described above, by docketing thenavigation unit 72 a, 72 b of the surgical object and/or the positionregistration unit 80 to the calibration unit, which has a fixed knownposition in the second coordinate system. Then, the position of thesurgical object and/or the position registration unit 80 is tracked bymeans of the navigation unit 72 a, 72 b. The position and orientationmay be tracked e.g. by comparing consecutive measurements of thecoordinates of the surgical object 77. Any difference between theconsecutive measurements is an indication of a movement. The trackedmovement, such as consecutive coordinates of the surgical object, may becommunicated from the surgical object to the data processing unit 74.Tracking movement of the surgical object may 77 comprise trackingmovement using at least one gyro and at least one accelerometer or anoptical tracking system to generate positional data as has beendescribed above. Furthermore, the communication of the positional andorientation data from the surgical object 77 to the data processing unit74 may be made wirelessly via the communication units 73 a and 73 b.Furthermore, the surgical object may comprise a surgical tool or asurgical template, the position or positions and/or orientation of whichhas been planned. Hence, tracking the position and/or orientation of thesurgical instrument may comprise tracking the position and/ororientation of at least one of a surgical tool and a surgical templatewithin the second coordinate system, and subsequently displaying theindication of a position and/or movement of at least one of the surgicaltool and the surgical template within the first coordinate system. Inother embodiments, positions of one or several surgical tools and/or oneor several surgical templates are tracked in the second coordinatesystem, and the position and/or movement is translated into anindication of the position and/or movement in the first coordinatesystem.

The first coordinate system and the second coordinate system maycomprise a polar and/or a Cartesian coordinate system.

Position and orientation information may be transmitted between theunits of the system at a frequency that is higher than 2 Hz, preferablehigher than 10 Hz. The communication hub may have a computational powerto be able to calculate and update the position and orientation at afrequency of 2 Hz, preferably 10 Hz, from all units to which it isconnected. Hence, the feedback to the surgeon will be updatedsufficiently such that corrections regarding the position and theorientation of the surgical object may be made based on all units thatare operative in the system during the procedure. Hence, thecommunication hub 4 is adapted to communicate the information betweenthe various units to which is connected at this frequency. Thecommunication hub 4 may, hence, substantially communicate the positionand orientation of a surgical object and a patient structure in thecoordinate system in which it is located to all other units to which itis connected. Hence, positional and orientation information may becommunicated between surgical objects and position registration unitspresent in the system. On a display, such as display 5, it is possibleto follow the position of all units in the system in relation to thepatient structure or structures as well as the relative positionsbetween the various units.

Feedback

FIGS. 8 and 9 illustrate embodiments of the pre-operative plan with thefirst path 40 and the second path 41 together with the data of thevirtual structure 30. The data is rendered on a display that may bevisible to the surgeon during surgery, and thus may included in thefeedback device. The coordinate systems of the patient and thepre-operative plan have been aligned, and the position of the surgicalobject calibrated if needed. At least a portion of the data of thepre-operative plan, and in relation thereto, position and orientationinformation of the surgical object in the second coordinate system isdisplayed in the first coordinate system represented by a currentposition of the virtual object and based on the tracked position andorientation of the surgical object.

In the embodiment of FIG. 8, a virtual object in the form of a virtualsurgical instrument 80 is shown in the display. The position andorientation of the virtual surgical instrument 80 relative to thevirtual structure 30 in the first coordinate system, i.e. the coordinatesystem of the planning unit 1, corresponds to the position andorientation of the surgical instrument relative to the patient structurein the second coordinate system, i.e. the coordinate system in which thepatient is present. In this embodiment, the feedback of the position andorientation of the surgical instrument in the second coordinate systemis the display of the current position and orientation of the virtualsurgical instrument 80. Hence, as the surgical instrument moves in thesecond coordinate system, the virtual surgical instrument 80 will movein real time in the first coordinate system relative to the virtualstructure 30, which will be shown on the display. Hence, since the firstpath 40 and the second path 41 are also displayed, the surgeon canmonitor in real time whether the surgical instrument is correctlypositioned and oriented relative to its planned positions andorientations, and if not correct its position to follow the path. Inthis embodiment, the virtual surgical instrument 80 is shown in a firstposition relative the first path 40 and in a second position relative tothe second path 41. This is for illustrative purposes on order toindicate different stages of the surgery. In other embodiments, however,multiple indications of movement of multiple virtual surgicalinstruments, possibly of different types, may be shown at the same timein the first coordinate system.

In the embodiment of FIG. 9, feedback of the tracked positions andorientations of the surgical object in the second coordinate system isindicated as a trace 81 in the first coordinate system. As isillustrated therein, before the surgical object has reached the entryposition 42, it deviates quit significantly from the planned path 41.However, since the planned path 41 extends before the entry point, thesurgeon is guided towards the planned path 41 and is able to follow theplanned path 41 between the entry position 42 and the end position 43.The trace 81 may be displayed in a different colour than the plannedpositions and orientations represented by the paths 40, 41. Furthermore,a warning indication may be displayed as feedback if the position of thesurgical object deviates more than an allowed amount from the plannedpositions and orientations. The allowed amount may be predetermined suchas fixed, system dependent, depending on type of surgical procedure,etc., or set during planning. The warning may e.g. be a visible warning,such as the trace 81 may shift colour from red to green when within theallowed rang or shape to bolder when outside allowed range. Additionallyor alternatively, the warning may be acoustic, such as an alarm. Thewarning indication may in other embodiments be provided separate fromother embodiments of the invention as described herein. In the contextof the invention, it provides for a more robust and reliable surgicalnavigation system.

For an implant procedure, the feedback may be used to verify a correctposition and orientation of the implant relative to the patientstructure. For example, the position of the implant may be registered asdiscussed above, using the position of a surface thereof that can becaptured using a position registration unit, such as a positionregistration probe, for example a tracked probe. Then, actual positionof the implant relative to the patient structure can be compared to theplanned position and orientation of the virtual representation thereofrelative to the virtual structure representing the patient structure.The implant may e.g. comprise one or several landmarks that are known tobe visible after implantation of the implant and yet having beingarranged in known predetermined positions on the implant. This may speedup registration of the position and orientation of the implant, sinceregistration process for a captured point cloud thereof is relativelycomputational simple. This can for example be used for checking positionand orientation of a femur component relative to a femur, and acetebularcup relative to an acetabulum.

Calibration

FIGS. 10a-10c illustrate embodiments of a surgical navigation systemcomprising a calibration unit 91. The calibration unit 91 may be aposition calibration unit 91 adapted to calibrate the position of anynavigation unit within the surgical navigation system. As discussedabove, calibrating the navigation unit allows for calibrating theposition of the surgical object 93, such as an end-effector 94 thereof,and/or a position registration unit 180, such as the positionregistration probe, thereof. The surgical navigation system is providedwithin the surgical theatre or operating room. Furthermore, the surgicalnavigation system may be adapted to track the position of navigationunit, and thus the surgical object and/or position registration unit,such as illustrated in FIG. 10c . The calibration unit 91 may beassociated with and/or comprise the second coordinate system, which maybe referenced to the first coordinate system. Alternatively oradditionally, the calibration unit 91 may have a fixed position withinthe surgical navigation system and thus within the second coordinatesystem, such as described above. The calibration unit 91 has a fixedposition within the second coordinate system when it is used forcalibrating the position of various objects, as will be described below.

In some embodiments, the calibration unit 91 is provided as a docketingstation. The origin of the second coordinate system may be providedwithin the calibration unit. Alternatively or additionally, the positionof the calibration unit 91 within the second coordinate system may beregistered. The calibration unit 91 is adapted to calibrate the positionof at least one of the surgical object 93, the navigation unit thereof112 a, a detachable navigation unit as discussed above, other tools, aswill be described below, and/or the position registration unit, withinthe surgical navigation system, such as within the second coordinatesystem. In more detail, each object to track may comprise a navigationunit 112 a. Before the surgery commences, the position of the navigationunit 112 a may be calibrated, i.e. its position and/or orientationwithin the operating room may be registered. Thus, the position andorientation of the navigation unit 112 a relative to the surgical objectmay be determined and tracked, i.e. dynamically referenced. For example,the position and orientation of the navigation unit 112 a may have afixed position and orientation relative an end effector of the surgicalobject and/or the position registration probe of the positionregistration unit. After calibration of the position and/or orientationof the navigation unit 112 a is made, the position and orientation ofthe navigation unit 112 a, and hence the position and orientation of thesurgical object and/or position registration unit, may be tracked inspace as will be discussed in more detail below.

Once the position of the navigation unit 112 a within the navigationsystem has been calibrated, the position of the navigation unit 112 awithin the second coordinate system may be tracked and its position orthe position of the surgical object translated into a position withinthe first coordinate system.

Similarly, the position registration unit 180 may comprise thenavigation unit 112 b. The position registration unit 180 may comprise asensor, such as the position registration probe. The positionregistration probe may activate the navigation unit 112 b of theposition registration unit 180, whereby positions from the surface ofthe patient structure may be obtained. The position registration probemay e.g. by a touch sensitive probe, whereby a tip thereof activates thenavigation unit 112 b, such that its position is determined while thetip touches a surface, such as a surface of the surgical structure.Alternative, the position registration unit 180 may comprise anactuator, such as a button, to activate the navigation unit 112 bthereof. Thus, a point cloud may generated, such as described above andmay be used to register the patient structure to the virtual structure.The registered information about the patient structure is registered tothe virtual structure. Furthermore, the registered surface data may bepresented aligned with the virtual structure by the output device, suchas the display 10. Hence, any deviation between a virtual structureobtained from the plan data and a virtual structure obtained from theregistered surface data may be indicated on the feedback device.

In some embodiments, such as illustrated in the embodiment of FIG. 10a ,at least one patient structure navigation unit 112 c, 112 d is attachedto the patient structure during the surgical procedure. The patientstructure navigation unit 112 c, 112 d may be attached to a pin or rodor any other device proving a relatively fixed position for thenavigation unit and that may be attached to a bony anatomy of thepatient that has a fixed relationship to the patent structure subject tothe surgery. While obtaining the positions from the surface of thepatient structure, the position of the navigation unit 112 c, 112 dattached to the patient structure within the second coordinate system isalso registered. Hence, each point of the point cloud representing thesurface of the patient structure may be related to the patient structurenavigation unit 112 c, 112 d. During surgery, the position of thepatient structure navigation unit 112 c, 112 d may be tracked wherebythe position of the patient structure is also tracked, i.e. dynamicallyreferenced, since there is a fixed relationship there between. This hasthe benefit that the surface of the patient structure does not have tobe in the line of sight of a position receiver of the surgicalnavigation system. Furthermore, if the exposed surface during surgerycomprises relatively little bony surfaces and more cantilever surfacesand the patient data has been obtained using CT, the system becomes morerobust and reliable, since a optical system, such as a camera, fortracking a surface captures the cantilever surfaces. CT has oneresolution where cantilever is not captured, whereas the optical systemhas a different resolution where cantilever is captured, wherein theregistration and referencing of the patient structure is inaccurate.According to embodiments of the invention, very little bony anatomy maybe captured at the same time as the patient structure navigation unit,wherein the accuracy and robustness of the system is superior.

FIGS. 11a-11e illustrates embodiments of the calibration unit. In theseembodiments, the calibration unit 191 comprises a base unit 192 a, 192b, 192 c for positioning the calibration unit 191 at an arbitrarilyposition within the surgical navigation system. The calibration unit,such as at the base unit 192 a, 192 b, 192 c, comprises an externalsurface for receiving a surface of the surgical object 93, such as asurface of a surgical instrument, for example an end-effector thereof.The external surface of the calibration unit 191 may have apredetermined shape, such as may comprise a recess or protrusion 193 a,193 b, illustrated in phantom lines in FIGS. 11a-11e . The surface witha predetermined shape may be symmetrical, such as half-spherical or domeshaped. Alternatively, the surface with a predetermined shape isasymmetrical. In the embodiment of FIGS. 11b-11c , the calibration unit191 b, 191 c comprises a navigation unit 194 a, 194 b. The position ofthe external surface for receiving the surface of the surgical objectrelative the navigation unit 194 a, 194 b of the calibration unit 191may be fixed and known. Hence, the position of the external surface forreceiving the surface of the surgical object within the secondcoordinate system is known or may be determined by registering theposition of the navigation unit 194 a, 194 b of the calibration unit.

In the embodiment of FIG. 11c , the base unit comprises an actuator 196,such as a switch, for initiating the registration process forregistering the position of the end-effector. The actuator 196 may belocated at the external surface for receiving the surface of thesurgical object, such as within the recess or at the protrusion. Whenthe end-effector is positioned at the external surface it may activatethe actuator 196, such as closing the switch, to initiate theregistration process. When the end-effector is removed from theactuator, the registration process is ended.

FIGS. 11d-11e illustrate an embodiment for registering a position of thesurgical object 93 or the position registration unit in the secondcoordinate system. The surgical object 93 may comprise the end-effector195, such as the tip of an instrument or tool, and the positionregistration unit may comprise the position registration probe. Tocalibrate the position in the second coordinate system, the end-effector195 is positioned at the recess or protrusion, such as within the recessor over the protrusion, such that it has a substantially fixed positionat one point and/or in one plane, e.g. the x-z plane, illustrated inFIG. 11d . The surgical object 93 also comprises navigation unit 112 a,such as described above. Then, as is illustrated in FIG. 11e , theposition of the end-effector 195, and optionally an longitudinal axisrelative the end-effector, such as of the instrument or tool, may beregistered while moving the surgical object 93 in at least a secondplane, such as the x-y plane and/or y-z plane, and while theend-effector 195 is positioned at the external surface, i.e. has arelatively fixed position in one point or one plane, such as the x-zplane, and at the same time multiple positions of the navigation unit isregistered. The registered positions of the navigation unit 112 a formsa shape, such as a dome shape, having an origin located at the positionof the end-effector 195 and with a radius determined by the distancebetween the origin and the registered positions. Hence, the registeredpositions of the navigation unit 112 a may be used to determine theposition of the end-effector 195 and the longitudinal axis of theinstrument or tool. In FIG. 11e , the surgical object 93 is shown inmultiple positions for illustrative purposes.

In some embodiments, the position of the end-effector relative to thenavigation unit of the object carrying the end-effector is known. Insuch an embodiment, the position of the navigation unit is calibrated bythe positioning the end-effector in the recess or protrusion andregistering the positions of the navigation unit of the moveable device,such as the surgical object or position registration unit, and theposition of the navigation unit of the calibration unit. The position ofthe recess or protrusion relative the navigation unit of the calibrationunit is known, wherein the position as well as the orientation of theend-effector may be determined based on the known position of theend-effector relative the navigation unit carried by the moveable objectand the registered position of its navigation unit and the registeredposition of the calibration unit.

The actuator may be connected to a communication unit 197, which in turnis connected to the communication hub 4. Furthermore, the communicationhub 4 may be connected to the position registration unit. Hence, theposition registration unit and associated processes for determining thepositions of the various devices of the system may be initiated byclosing a circuit connected to the actuator 197. The calibration unit191 may be connected to the communication hub using a wired or wirelessconnection, such as a WiFi or Bluetooth® communication unit.

FIG. 12 illustrates a detachable navigation unit 198. The detachablenavigation unit 198 comprises a surface that can be positioned at thebase unit in a fixed positional relationship. The connection interfacethere between may have a shape such the detachable navigation unit 198has a fixed positional and orientational relationship to the calibrationunit. This may be achieved using one or more protrusions (illustrated inphantom in FIG. 12) 199 a, 199 b, 199 c and recesses 199 d, 199 e, 199 fhaving complementary shapes. A corresponding connection interface may beintegrated with the object to carry the navigation unit, such as thesurgical object or the position registration unit. The position of thedetachable navigation unit 198 may be calibrated by registering itsposition relative the connection interface of the calibration unit, suchas utilizing any of registration technique described above relativeFIGS. 11a-11d . Once the position of the detachable navigation unit 198is determined, it may be connected to the object to carry. The type ofobject that fits to the detachable navigation unit 198 may bepredetermined, such as programmed within a memory of the detachablenavigation unit 198, or defined utilizing the input device. Furthermore,the position of the end-effector relative to the detachable navigationunit 198 may be known. This may also be used with a navigation unitintegrated with the object. Hence, the position of the end-effector maybe tracked when the detachable navigation unit 198 is attached to theobject to carrying it.

As is illustrated in FIGS. 10a-10c , the surgical navigation system maybe adapted to track the position of multiple objects. The surgicalnavigation system comprises the calibration unit 91, such as describedin the embodiments of FIGS. 11a-11d and 12, respectively. The positionof a surgical object 93 in the form a surgical instrument may becalibrated and tracked, such as described above. Another surgical objectis a position registration unit 180. Furthermore, another device is thepatient structure navigation unit 112 c, 112 d attachable to the patientstructure. In this embodiment one patient structure navigation unit 112d is attached to the femur and another patient structure navigation unit112 c to the pelvis. Hence, if the patient moves after registration ofthe positional information of the surface of the patient structuretogether with its patient structure navigation unit 112 c, 112 d, theposition of the patient structure is tracked. The surgical navigationsystem also comprises a feedback unit, such as a display 300. Thepatient structure may be aligned with the virtual structure, such asdescribed above. Utilizing the components of the surgical navigationsystem, the position of the surgical object relative to thepre-operative plan and the patient structure may be tracked inreal-time, such as illustrated in FIG. 11c , wherein the position of thevirtual object is displayed in relation to the virtual structure in thesame relationship as the surgical object 93 to the patient structure.Furthermore, by calibrating the navigation unit 112 a of the surgicalobject, and thus the position of the end-effector, the accuracy,robustness, and reliability, and flexibility of the system is enhancedcompared to an uncalibrated system or a system wherein the calibrationis based on scanning the surgical object and registering against CADobjects.

The calibration unit provides for tracking a standard surgical object ofarbitrary shape, to which a position sensor is attached at any positionthereof. By registering the position of the navigation unit of thesurgical object at a known position of a calibration unit, the positionof the end-effector may be determined. Hence, the position of theend-effector is calibrated against at least one known position of thecalibration unit. The position may be calibrated by calculating theposition, such as described above in relation to the embodiments ofFIGS. 11a-11d , or it may be predetermined, such as described relativeto the embodiments of FIG. 1. Hence, the system according to theinvention may be integrated with any surgical object, such as surgicaltools and instrument, that are on the marked and no special purposeinstruments and tools may be acquired. Hence, the system is veryflexible and can be implemented at a low cost. Furthermore, calibrationof the components of the system is flexible and efficient.

The processes and systems described herein may be performed on orencompass various types of hardware, such as computer systems. In someembodiments, computer, display, and/or input device, may each beseparate computer systems, applications, or processes or may run as partof the same computer systems, applications, or processes—or one of moremay be combined to run as part of one application or process—and/or eachor one or more may be part of or run on a computer system. A computersystem may include a bus or other communication mechanism forcommunicating information, and a processor coupled with the bus forprocessing information. The computer systems may have a main memory,such as a random access memory or other dynamic storage device, coupledto the bus. The main memory may be used to store instructions andtemporary variables. The computer systems may also include a read-onlymemory or other static storage device coupled to the bus for storingstatic information and instructions. The computer systems may also becoupled to a display, such as a CRT or LCD monitor. Input devices mayalso be coupled to the computer system. These input devices may includea mouse, a trackball, or cursor direction keys.

Each computer system may be implemented using one or more physicalcomputers or computer systems or portions thereof. The instructionsexecuted by the computer system may also be read in from acomputer-readable medium. The computer-readable medium may be a CD, DVD,optical or magnetic disk, laserdisc, carrier wave, or any other mediumthat is readable by the computer system. In some embodiments, hardwiredcircuitry may be used in place of or in combination with softwareinstructions executed by the processor. Communication among modules,systems, devices, and elements may be over a direct or a switchedconnection, and wired or wireless networks or connections, via directlyconnected wires, or any other appropriate communication mechanism. Thecommunication among modules, systems, devices, and elements may includehandshaking, notifications, coordination, encapsulation, encryption,headers, such as routing or error detecting headers, or any otherappropriate communication protocol or attribute. Communication may alsomessages related to HTTP, HTTPS, FTP, TCP, IP, ebMS OASIS/ebXML, securesockets, VPN, encrypted or unencrypted pipes, MIME, SMTP, MIMEMultipart/Related Content-type, SQL, etc.

Any appropriate 3D graphics processing may be used for displaying orrendering including processing based on OpenGL, Direct3D, Java 3D, etc.Whole, partial, or modified 3D graphics packages may also be used, suchpackages including 3DS Max, SolidWorks, Maya, Form Z, Cybermotion 3D, orany others. In some embodiments, various parts of the needed renderingmay occur on traditional or specialized graphics hardware. The renderingmay also occur on the general CPU, on programmable hardware, on aseparate processor, be distributed over multiple processors, overmultiple dedicated graphics cards, or using any other appropriatecombination of hardware or technique.

As will be apparent, the features and attributes of the specificembodiments disclosed above may be combined in different ways to formadditional embodiments, all of which fall within the scope of thepresent disclosure.

Conditional language used herein, such as, among others, “can,” “could,”“might,” “may,” “e.g.,” and the like, unless specifically statedotherwise, or otherwise understood within the context as used, isgenerally intended to convey that certain embodiments include, whileother embodiments do not include, certain features, elements and/orstates. Thus, such conditional language is not generally intended toimply that features, elements and/or states are in any way required forone or more embodiments or that one or more embodiments necessarilyinclude logic for deciding, with or without author input or prompting,whether these features, elements and/or states are included or are to beperformed in any particular embodiment.

Any process descriptions, elements, or blocks in the flow diagramsdescribed herein and/or depicted in the attached figures should beunderstood as potentially representing modules, segments, or portions ofcode which include one or more executable instructions for implementingspecific logical functions or steps in the process. Alternateimplementations are included within the scope of the embodimentsdescribed herein in which elements or functions may be deleted, executedout of order from that shown or discussed, including substantiallyconcurrently or in reverse order, depending on the functionalityinvolved, as would be understood by those skilled in the art.

All of the methods and processes described above may be embodied in, andfully automated via, software code modules executed by one or moregeneral purpose computers or processors, such as those computer systemsdescribed above. The code modules may be stored in any type ofcomputer-readable medium or other computer storage device. Some or allof the methods may alternatively be embodied in specialized computerhardware.

It should be emphasized that many variations and modifications may bemade to the above-described embodiments, the elements of which are to beunderstood as being among other acceptable examples. All suchmodifications and variations are intended to be included herein withinthe scope of this disclosure and protected by the following claims.

The present invention has been described above with reference tospecific embodiments. However, other embodiments than the abovedescribed are equally possible within the scope of the invention.Different method steps than those described above, performing the methodby hardware or software, may be provided within the scope of theinvention. The different features and steps of the invention may becombined in other combinations than those described. The scope of theinvention is only limited by the appended patent claims.

The invention claimed is:
 1. A system for computer assisted orthopedicfeedback of a surgical object relative a pre-operative plan, thesurgical object being moveable relative to a patient structure duringsurgery; said system comprising: at least one camera, a positionregistration probe having an end-effector, a first tracking unitattachable to the position registration probe, a surgical instrumenthaving an end-effector, a second tracking unit attachable to thesurgical instrument, a position registration unit, and a calibrationunit, wherein said position registration unit comprises said at leastone camera, and is adapted to obtain at least one position of thepatient structure based on multiple positions of the positionregistration probe, at least one of the first tracking unit beingdetachable relative the position registration probe and the secondtracking unit being detachable relative the surgical instrument; and thecalibration unit is adapted to calibrate a position of the end-effectorof at least one of the position registration probe, when the firsttracking unit is attached thereto, and the surgical instrument, when thesecond tracking unit is attached thereto, within the system.
 2. Thesystem according to claim 1, wherein the first tracking unit isdetachable relative the position registration probe, and the secondtracking unit is detachable relative the surgical instrument.
 3. Thesystem according to claim 2, wherein the calibration unit is adapted tocalibrate the position of the end-effector of the position registrationunit and the end-effector of the surgical instrument within the system.4. The system according to claim 1, wherein the first tracking unit isnon-detachable relative the position registration probe and the secondtracking unit is detachable relative the surgical instrument.
 5. Thesystem according to claim 4, wherein the calibration unit is adapted tocalibrate the position of the end-effector of the surgical instrumentwithin the system.
 6. The system according to claim 1, wherein saidfirst tracking unit and said second tracking unit each comprises severalposition determination units.
 7. The system according to claim 6,wherein each position determination unit comprises an optical component.8. The system according to claim 1, wherein the calibration unitcomprises a docketing station having an origin.
 9. The system accordingto claim 1, wherein the calibration unit comprises at least one surfacehaving a predetermined position for receiving the end-effector of atleast one of the position registration probe and the surgicalinstrument, and at least one predetermined shape for positioning saidend-effector in at least one substantially fixed position.
 10. Thesystem according to claim 9, wherein the calibration unit comprises anavigation unit including a position sensor having a fixed positionalrelationship relative the surface with a predetermined position, thesurface with a predetermined position having a shape to position theend-effector in at least one plane or position, and the positionregistration unit is adapted to register at least one position of atleast one of the first tracking unit, when attached to the positionregistration probe, and the second second tracking unit, when attachedto the surgical instrument, and when said end-effector is positioned atsaid at least one plane or position.
 11. The system according to claim1, further comprising a feedback device adapted to provide feedback of acurrent position and orientation of the surgical instrument relative toa planned position and orientation of a virtual object in response to atracked position and orientation of the surgical instrument, wherein thefeedback device comprises at least one of: an indicator, which isintegrated with the surgical instrument and adapted to provideindication of a deviation of a current position and orientation of thesurgical object relative the planned position and orientation of thevirtual object, wherein the indicator comprises a visual indicator, atactile indicator, and/or an audio indicator; a visual indicator adaptedto provide, on a display, visual feedback of a current position andorientation of the virtual object relative to the planned orientationand position of the virtual object in response to tracked position andorientation of the surgical instrument; a visual indicator adapted toprovide, on a display, visual indication of a deviation of a currentposition and orientation of the virtual object relative the plannedposition and orientation of the virtual object in response to trackedposition and orientation of the surgical instrument; and a visualindicator, which is integrated with the surgical instrument and adaptedto provide visual indication of a deviation of a current position andorientation of the surgical instrument relative the planned position andorientation of the virtual object.
 12. The system according to claim 1,further comprising a third tracking unit attachable to the patientstructure.
 13. The system according to claim 12, wherein third trackingunit includes a position sensor adapted to track a current position andorientation of the patient structure.
 14. The system according to claim13, wherein said third tracking unit is attachable to the patientstructure at a fixed position relative to the patient structure, andsaid position registration unit is adapted to obtain positions of thefirst tracking unit and the third tracking unit simultaneously when thefirst tracking unit is attached to the position registration probe andwhen the third tracking unit is attached to the patient structure. 15.The system according to claim 1, wherein the tracking unit comprises anoptical navigation system, and a communication device adapted totransfer tracking data to a communication hub.
 16. The system accordingto claim 1, further comprising a planning unit comprising a computer andbeing adapted to provide a virtual object, which is a virtualrepresentation of the surgical object and comprising at least one of avirtual surgical instrument and a virtual implant, a virtual structure,which is a virtual representation of the patient structure, and apre-operative plan including a planned position and orientation of thesaid at least one of a virtual surgical instrument and a virtual implantrelative to the virtual structure, and being adapted to register thepatient structure to the virtual structure.
 17. The system according toclaim 16, wherein the planning unit is adapted to provide apre-operative plan based on CT data obtained from a patient comprisingthe patient structure.
 18. The system according to claim 1, wherein atleast one of the first tracking unit and the second tracking unitcomprises a connection interface, which has at least one of projectionsand recesses such that the connection interface of the tracking unitfits a connection interface on at least one of the position registrationprobe or the surgical instrument, said connection interface of theposition registration probe or the surgical instrument having a shapethat is complementary to the shape of the connection interface of thetracking unit.